Electric furnace resistor element



March l5, 1932. F. A. FAHRENWALD ELECTRIC FURNACE RESISTOR ELEMENT Filed July 11, 195o Patented Mar. 15, 1932 PATENT OFFICE FRANK A. FAHRENWALD, OF CHICAGO, ILLINOIS ELECTRIC FURNACE Application filed July 11,

This invention relates to industrial furnaces of the kind in which the required heat is developedby electric resistance, and has for its object to provide a form of resistor or resistance grid which can be produced to good advantage by foundry methodsl from high heat resisting alloy, and which will have the capacity of retaining its form and integrity when produced in the form of a series of connected loops as if the resistance strip were doubled upon itself, and mountedupon conventional or other suitable supports carried by the furnace Wall, for instance, in-

wardly projecting hangers over which the respective upper doublings of the grid may be engaged and from which the loops of'depending members will remain in suspenslon.

Resistors consisting of Hat strips of flexible material wound in serpentine form about upper and lower spaced projections on the inner furnace wall of an electric furnace have long been used in electric resistance furnaces. But resistors of this type are subject to injury in use, besides requiring sustention 'and guidance at their lower as well as their upper loops, and they are objectionable for other reasons. Resistors of massive form have also been used, produced by foundry methods, and such resistors have been designed with special sections adapting them to retain their form under the distorting stresses ofhigh temperature, but few of these forms are suitable for the purpose owing to the problem of maintaining uniform density throughout the resistor under cooling problems at the time of casting.

The present invention has for its obj ect to provide a special section for resistors or ids used in electric furnaces, which section will afford high eciency in retention of form against distorting stresses at high tempera tures; one which will be an easy section to cast with uniform density of metal throughout, and will lend itself with advantage to embodiment in a resistance grid comprising a number of vertical loops as well as to conu venient suspension upon existing hangers or mounting means found within-conventional types of electric furnace.

5 The invention consists in making there- RESISTOR ELEMENT 1930. Serial No. 467,219.

radiation, rigidity of doublings or loops of the grid, and its capacity to 'sustain itself in suspension. ln the accompanying drawings- Figure l is a sectional view showing the interior of a conventional electric furnace with a known form of hanger or gridsuspending means upon which a resistor or grid embodying the features of the present invention is installed. f

Figure 2 is a section on line 2cv- 2m of Figure 1.

Figure 3 represents a modified means for suspending the grid; and

Figures 4, 5, and 6 illustrate Variations in the design of a resistor of arcuate section.

A represents a portion of an electric furnace built of masonry, B represents hangers projecting from the walls of such furnace, r

and C represents a circuit connector, all of which may be of known construction.

Mounted upon the hangers B is a resistor element 1 given the form of a grid comprising a series of parallel vertical legs la united by upper doublings or loops 2 and lower doublings or loops 3. Such a grid ma be supported in the furnace by leaving 1t in suspension with its upper doublings 2 engaged over supports B, or it may be equipped with a hanger 4 (Figure 3) having a form especially adapted to the resistor section andconstructed with an eye 5 by which it may be hung upon the support B.

In order to make the resistor l rigid against distortion under the influence of heat, a large part of its section is given a direction or directions at substantial angles to the general plane ofthe grid which the resistor forms; but the several portions of the resistor sections are merged together without angles of meeting and preferably Without material change in the thickness of the metal. This is due to the fact that the section of the resistor is arcuate in form, being either a simple arc of a circle as illustrated at in Figure 2 Where the are is substantially a semi-circle or at lg/ in Figure 5 Where a segment is employed that is considerably less than a semicir'cle, or a complete are as shown at le in lo Figure 4 Whereit is substantially one-half of an ellipse divided on its major axis; or it may be of other arcuate forms appropriate to the `avoidance of abrupt cnanges in direction or Ythiclnaess of metal. is suggested in Figure i5 6, some of the lines t `he section of the resistor be straight lines, as in the production of "ie web portion 1w stii'ening ilanges ly, long as 'he liange portion and web portion are unit i by arcs of suliicient 'te radius to avoid abrupt changes in directionn An important feature of the invention incident to the various designs which may be employed, is `that the resistor may be cast With its hollow side up, and when so Cast,

all inclined or upwardly extending portions Will stand in such reiacion to the lowermost portion as will insure solidication of the metal under the indu-ance of gravity at the time the cast is cooled; and a portion of the E0 lines along the middle or web portion of the body which lies horizontal in casting may even he straight if the upwardly extending parts are sucient 1n mass to make eliective risers in feeding molten metal toward the middle of the casting; and, of course, the upstanding of Hange-like portions, so lon as they merge with the web-like portlons through means of arcuate portions, can include straight lines as illustrated in Figure 6. The form of section shown in Figure 6 is intended to be included in the term substantially arcuate section.

I claim: A heat-developing resistor for electric furnaces, comprising an integral casting of heat resisting material having massive section and comprising a series of members united by curved portions, the section of the resistor throughout, and including the curved portions, being of uniformly curved channel form', free from angles or abrupt deiections. Signed at Chicago, Illinois, this 1st day of July, 1980.

FRANK A. FAHRENWALD. 

